Haki + dc universe + green lantern
Haki and green lantern both work off of willpower. So they can strengthen each other, so that the green lantern power would be more,potent? Or they can combine to make something more than the sum of the two parts. Or maybe they both can be used separately or together. I think full powered haki is stronger than full power green lantern, in the physical aspect. The green lantern works off of willpower but it doesn't directly enhance the body. The green lantern uses willpower as a fuel source to make projections l, force fields , fly but that's just coating oneself with a force field and moving said force field. In any case I think the 2 would work together wonderfully.
Haki + dxd
Sounds like an interesting idea, I just don't know enough about dxd
Haki + Harry Potter universe
Sounds very out of place, kinda like that one anime where everyone is a wizard with lines on their face and this guy is a bodybuilder aka Saitama mk2, but this time he can also use spells .
Haki + danmachi, aka Is It Wrong to Try to Pick Up Girls in a Dungeon?
Would work well, character can either go the swordsman route or the fist fighter route or the ranged or maybe all 3. Might not even need armor.
Haki + baki universe
Probably would be super op in this universe
Haki + the eminence in shadow
I AM ATOMIC/DEATH
very op especially if it can be taught to others and they wouldn't need to be worried about getting stabbed like when he was in the sanctuary
Haki + fairytail universe
Could be a gilgarts type of wizard
Haki + starwars
They might be able to hold a lightsaber bare handed. Might even be able to control both the darkside and lightside of the force through their unyielding willpower. With observation haki they can never get shot by a blaster, might even have future sight but that's kinda similar to the force where they get visions.
Haki + more ides post here